Industrial applications of the present invention relate to the construction of trusses for small and large spanning bridges, trusses for other structures that need support (comprising industrial warehouses). Finally, the same design can be used for lattice structures, such as scaffolding of any kind, comprising scaffolding for renovation projects that require a “cage”.
After the well-known collapse of the Tacoma bridge in 1940, the designers of bridges have felt the need to reinforce the road bed with metal trusses that would dampen oscillations. In the Tacoma bridge two types of oscillations were visible: the longitudinal and torsional ones. Those that caused the collapse were certainly of the torsional type, which in turn were generated by the longitudinal ones.
Immediately after the collapse of the bridge in Tacoma, there have been several attempted explanations, starting from possible mathematical theories. But there have not been significant modeling progress. The reason is certainly to be attributed to the enormous difficulties of the theory of elasticity; many relatively simple problems still remain unanswered. In addition, the growing awareness of the strong nonlinearities in the oscillatory behavior of bridges, has dissuaded many generations from seeking precise theories. To date there is not a theory that accurately describes the oscillatory behavior of the bridges that neither is able to fully explain the collapse of the Tacoma bridge.
Subsequently, several other bridges have shown strong oscillations that, in some cases, have led to their collapse.
It is therefore necessary to find the best way to mitigate the longitudinal oscillations and prevent the formation of torsional oscillations. It is clear that both oscillations can be eliminated with very stiff, heavy and expensive trusses. Recently the problem has been raised of what could be the right balance between stiffness and economy; regarding economy which means not only the direct economy of material but also the indirect economy of a structure with a smaller mass and that needs support towers and cables with more modest performance.
To dampen the oscillations of the bridge, under the road bed are usually positioned horizontal metal trusses framed with different types of shapes, typically polygonal. There are two or more layers of these horizontal trusses connected to each other with vertical trusses or with frames, similar or different depending on the structure.
In the book of T. Kawada, titled “History of the Modern Suspension Bridge: solving the dilemma between economy and stiffness”, ASCE Press (2010), are reviewed reinforcement trusses of the existing suspension bridges and described ways to connect with each other the different truss segments. Among the shapes most frequently used are the squares 10, the equilateral triangles 11 and the rectangles isosceles triangles 12.